Collaborative XML Editing on Small Devices through Mobility Middleware Jaakko Kangasharju and Tancred Lindholm Captio is an XML editor for collaborative document editing that runs on small devices such as PDAs and high-end mobile phones. It supports both synchronous collaboration, where all changes are visible to all users in real time, and asynchronous collaboration, where changes are made privately and synchronized to everyone on reconnection. Captio is built on top of the Fuego mobility middleware, which provides an efficient XML serialization for messages, a publish/subscribe system for synchronous collaboration, an XML-aware synchronizer for asynchronous collaboration, and a reconfiguration service for switching between collaboration modes.